Transfusion of platelets is now a widely used form of therapy for the treatment of hemorrhage in thrombocytopenic and thrombocytopathic patients. It is indispensable in the protocol treatment programs for acute leukemia, aplastic anemia, platelet deficiency, as well as replacement therapy in major surgical procedures.
Platelets are separated from whole blood as platelet-rich plasma (PRP) by procedures involving centrifugation. Transfusion of platelets is accomplished most often in a form of platelet-concentrates (PC) which are prepared by the high speed centrifugation of PRP. Several units of blood are required to obtain a sufficient number of platelets for therapeutic effectiveness. The use of multiple donors increases risks of isoimmunization and transmission of disease. In order to procure enough platelets from a single donor, the technique of plasmapheresis is required in which platelet-poor plasma (PPP) and packed red blood cells (RBC) are returned to the donor's blood circulation. The commonly used procedure of slow speed centrifugation with the routine equipment found in any blood bank is cumbersome, very time-consuming, and yields platelets heavily contaminated with white blood cells (WBC) and RBCs and gave low patelet recovery. A considerable improvement in the procurement of platelets has been made by the use of specialized blood processing equipment, Haemonetics-30, which permits the collection of two to four units of PC from a single donor. In this procedure, known as plateletpheresis, blood is pumped directly from the donor through a rotary seal into a centrifuge plastic bowl. Blood components are separated by forming concentric bands which overflow from the bowl in a sequence, depending on their specific density. This technique, however, permits one to harvest on the average only 46 percent of platelets from the blood circulating in the bowl. In order to collect the 4.times.10.sup.11 platelets required for therapeutically effective transmission, at least 6 liters of blood must be processed, which takes from 2 to 3 hours of the donor's time. The operation is time-consuming and costly. Also, large initial investment for purchasing expensive equipment is required. Collected with this technique, platelets are heavily contaminated with WBCs and RBCs. Administration of PC contaminated with WBC may cause serious complications in patients. Platelets and WBC share HL-A antigens which are more immunogenic on WBC than those on platelets. As a result, WBC contamination may be responsible for the alloimmunization in patients which, in turn, causes with each consecutive transfusion progressive reduction in hemostatic effectiveness of platelets and, in more severe cases, may lead to post-transfusion thrombocytopenia. There are also systemic reactions which may occur within 20 minutes after completion of a platelet transfusion consisting of chills and fever. Antibodies to contaminating leucocytes are implicated in these reactions. Because of these side effects, removal of contaminating WBCs from PC by differential centrifugation is strongly recommended, which further complicates the procedure. Clearly, there is a need for improvement of platelet collection technique by making it safer and more effective in collecting PC at a higher yield, free of WBC and involving shorter time and lower cost than the present techniques offered.